FIG. 12 indicates a prior art flexure mounting of a reciprocating load "a" upon thin, resilient flexure strips S, S' cantilevered-up from a rigid base B. One, or several, such strips have been so used. However, one problem arises when it is vitally important to maintain load reciprocation perfectly rectilinear, since the normal tendancy is to pivot around such flexures in something of an arc (as in phantom FIG. 12). One object of this invention is to provide improved means for so mounting loads for more rectilinear reciprocation. Another object is to provide pairs of flexure mounts which are "self-bending" and are self-controlled to execute "S-bend" flexing.
Another related problem has been "coupling" of the distal end of such a flexure to the load. For instance, if such flexure strips are simply rigidly bonded to the load, little, if any, bending is possible and any substantial, prolonged bending tends to distort the strips or rupture the strip-load bond, or both--as well as to accentuate the (often undesired) arcuate travel of the load. One conventional approach to improving this situation is to bond the flexure end to an elastomeric insert and secure this insert firmly to the load arm, as indicated for rubber insert r bonded to the end of steel flexure strip S in FIG. 12A. But this has drawbacks. For instance, such an insert tends to "part" from load arm "a" more as the flexure pivoting excursion increases--distorting the rubber and stressing it as indicated in FIG. 12B; and obviously tending to rupture or unseat the resilient coupling.
Another drawback with such resilient couplings is that they introduce a "pivot point" at their junction with the load; also they tend to "slip" in various directions and allow undesirable "skew motions" (e.g., lateral slip, forward pitch, yaw, etc.) of the load. This is absolutely unacceptable in many applications; e.g., where the load-arm carries a tiny magnetic recording transducer (such as indicated at "h" in FIG. 3 which is understood as to be moved across "medium-locus" M . . . M by a load arm La supported for reciprocation on flexures pf, pf'). In such instances, the "skew motions" are not only antagonistic to accurate transducer positioning, but they also introduce non-linear drive/load coupling which upsets the servo system. That is, as the drive means reciprocates its load at relatively high gain (high frequency, large-excursion) and a damping feedback is experienced, it becomes virtually impossible for the servo system to maintain the desired transducer travel; also oscillation will likely result.
This invention is intended to provide improved flexure mountings alleviating such problems, especially as regards paired flexure mounts for magnetic transducers. That is, it is found, according to a feature hereof, that such flexure mounts may be advantageously provided in the form of resilient piezoelectric strips, or "pz-flexures".
Moreover, it is also found, according to a related feature, that such "pz-flexures" may be made, and controlled, to execute like "S-bends" when made in a prescribed "compound" configuration--whereby to better mount and guide such loads in more controlled, stable, rectilinear reciprocation. It is found that one may rigidly bond the driven end of such "pz-flexures" to a load-arm and drive the arm in such a manner (described below) that the flexures will both execute relatively smooth, low-stress "S-bends" as indicated schematically in FIG. 2. In an embodiment like that of FIG. 2, one can rigidly join a pair of "compound" piezoelectric flexure mounts (1, 1') to a load arm La, and--dispensing with the usual drive means--use such flexure mounts as a "motor" to reciprocate the load-arm "a" relatively rectilinearly. The while these pz-flexures will execute a smooth "S-bend" and will also serve as a relatively precise, convenient and advantageous reciprocator (drive) means for the load, while reducing problems with vibration and resonance. Such a pair of "compound pz-flexures" will also be seen to eliminate the usual troublesome "pivot point" mentioned above and will allow both ends of each flexure mount to be rigidly secured.
This invention will be seen as particularly apt with apparatus for establishing and maintaining the position of such transducers with respect to such recording tracks; and is particularly adapted for recording on magnetic tape, drum, and disk media, (especially with high density, high TPI recording). In such recording, a fast, non-magnetic, miniaturized, solid state translation means is particularly desired--especially where translation distances are relatively small (on the order of a few dozen microinches or more--e.g., typically over a total excursion of a few mils).
Workers in the art of magnetic recording at ultra-high densities are well aware of limitations in present-day transducer positioning apparatus, such as the typical voice coil actuator systems, or the like. Such systems are undesirably large, slow and unwieldly. They are particularly unsatisfactory for "centering" a transducer relative to a narrow recording track, where positioning is critical. Such systems are also troublesome in that they use solenoid magnets or other magnetic actuator means, creating stray magnetic fields that can interfere with the magnetic recording apparatus. The present invention is adapted to remedy these shortcomings with a solid state, piezoelectric flexure arrangement for mounting and positioning magnetic heads.
Thus, it is an object of this invention to provide the mentioned features and advantages. Another object is to provide improved "paired-piezo-flexure" mounts. Another object is to provide such mounts as particularly adapted for fine-positioning and centering a transducer relative to a recording surface. Yet another object is to provide such a supporting/positioning solid state structure comprised of one or more electrostrictive elements adapted to be deformed (elongated and bent) into a "S-bend" in accordance with a control voltage pattern applied thereto--preferably using one or more pairs of "compound" piezo-flexures, mounted in parallel and adapted to translate the supported load structure relatively rectilinearly.